Numerical zymotaxonomy and variability of the internal transcribed spacers (ITS) between the small and large subunits of the rRNA genes were used to examine strain variation and relationships in natural populations of Leishmania (Viannia) braziliensis. A total of 101 strains from distinct hosts and Brazilian geographic regions were assigned to 15 zymodemes clustered in two major genetic groups. The great number of isolates (48.5%) placed in zymodeme IOC/Z-27 were collected on the Atlantic coast. The high molecular diversity found in populations in the Amazon Basin was related to the great number of sandfly vector(s) in that region. The results of the restriction fragment length polymorphism analysis of the ITS depicted considerable intraspecific variation. Genotypic groups A, B, and C contained 39, 40, and 22 isolates, which were divided into 16, 10, and 15 genotypes, respectively. The genetic polymorphism observed demonstrates the degree of diversity of L. Infections with the parasitic protozoan Leishmania (Viannia) braziliensis Vianna 1911 (Kinetoplastida: Trypanosomatidae) or strain variants are recognized as causing human illness in many areas of (sub)tropical America (at least 15 countries), where it constitutes a significant public health problem. Many of these parasites seem to have a unique life cycle, with different phlebotomine sandfly (Diptera: Psychodidae) vectors and/or animal reservoirs and a different geographic distribution (13). This pathogen is capable of producing a variety of clinical manifestations, such as (i) cutaneous leishmaniasis (CL), which may heal spontaneously; (ii) mucosal leishmaniasis (ML), a hyperergic invasive ulcerative form that progresses in the absence of any apparent cellular defect (15); and (iii) disseminated CL (4).Most of the environmental factors affecting the epidemiology of the various leishmaniases are still poorly understood. Wild mammals serve as reservoirs for most of the New World Leishmania spp. (21), but there is increasing evidence that some of the human pathogenic Leishmania strains can be maintained in both sylvan and urban cycles. In the case of L. (V.) braziliensis, the principal vertebrate hosts in the sylvan cycle have not been identified, but there is evidence that dogs, horses, and donkeys may serve as reservoir hosts of this parasite (15). The existence of an urban cycle involving peridomestic sandfly species for L. (V.) braziliensis reflects the ability of these parasites and their vectors to adapt to changes in their original forested habitats with important public health implications. Studies using molecular techniques to characterize L. (V.) braziliensis populations from different regions have shown a relationship between level of similarity among the parasite populations (12, 24) and their geographic range, but recent data have also indicated that the considerable variability detected among these parasites is more probably related to the sandfly vector(s) and/or animal reservoir(s) involved in the transmission cycles (18).Pathogens that produce...

Transfer of bloodstream-form Trypanosoma brucei variant 221a from calf serum to dog serum-based medium induces acute iron starvation, as the transferrin receptor (Tf-R) of variant 221a binds dog Tf poorly. We show here that transfer to dog serum induces a 3-5-fold increase in Tf-R mRNA and protein within one doubling time (8 h). Because iron stores are still high 8 h after transfer, we infer that the signal for Tf-R overproduction is the decreased availability of cytosolic iron when cellular iron import drops. Up to 30% of the extra Tf-R spills out of the flagellar pocket onto the pellicular surface. Because the 5-fold increase in Tf-R is accompanied by a 5-fold increase in bovine Tf uptake, the up-regulation of Tf-R levels in response to Tf starvation helps the trypanosome to compete for limiting amounts of Tf. We noted that Tf-R levels also vary in calf serum medium. Cells in dense cultures contain up to 5-fold more Tf-R mRNA and protein than in dilute cultures. Only onetenth of the extra Tf-R reaches the pellicular surface. The increase cannot be explained by a lack of Tf or to cell density sensing but is due to pericellular hypoxia. Our results show that bloodstream-form trypanosomes can regulate the expression of the two Tf-R subunit genes and the localization of their gene products in a flexible manner. This flexibility is made possible by the promoter-proximal position of the two genes in the variant surface glycoprotein expression site.The unicellular protozoan parasite Trypanosoma brucei can infect a broad range of mammals. It multiplies extracellularly in blood and escapes elimination by the immune system through antigenic variation of its surface coat, which consists of one major protein species, the variant surface glycoprotein (VSG), 1 attached to the plasma membrane by a glycosylphosphatidylinositol anchor (1, 2). African trypanosomes cover their iron need by taking up host transferrin (Tf) (3-5). Uptake occurs in the flagellar pocket (3, 6, 7), an invagination of the plasma membrane where all endocytosis and traffic to the trypanosome surface takes place (8 -12), and is mediated by a transferrin receptor (Tf-R), a heterodimer consisting of subunits encoded by expression site-associated gene (ESAG) 6 and 7 (13-17), which are located in the telomeric VSG gene expression sites (for review, see .The ESAG6 subunit of about 400 amino acids is attached to the plasma membrane by a glycosylphosphatidylinositol anchor; ESAG7 of about 340 amino acids remains membraneattached by holding on to ESAG6 (for review, see Ref. 22). The trypanosomal Tf-R resembles VSG dimers in apparent structure and (distantly) in sequence (23), and it is unlike other Tf-Rs in nature.

Protein kinase A (PKA)-induced estrogen receptor alpha (ERa) phosphorylation at serine residue 305 (ERaS305-P) can induce tamoxifen (TAM) resistance in breast cancer. How this phospho-modification affects ERa specificity and translates into TAM resistance is unclear. Here, we show that S305-P modification of ERa reprograms the receptor, redirecting it to new transcriptional start sites, thus modulating the transcriptome. By altering the chromatin-binding pattern, Ser305 phosphorylation of ERa translates into a 26-gene expression classifier that identifies breast cancer patients with a poor disease outcome after TAM treatment. MYC-target genes and networks were significantly enriched in this gene classifier that includes a number of selective targets for ERaS305-P. The enhanced expression of MYC increased cell proliferation in the presence of TAM. We demonstrate that activation of the PKA signaling pathway alters the transcriptome by redirecting ERa to new transcriptional start sites, resulting in altered transcription and TAM resistance.

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